(Electro)luminescent polymer-acceptor system comprising a polymer and an acceptor for transferring excitation energy

ABSTRACT

The invention pertains to an (electro)luminescent polymer-acceptor system comprising a polymer with a plurality of chromophores doped with an acceptor for transferring excitation energy from the polymer to the acceptor wherein at least one wavelength of the polymer emission is a wavelength at which the acceptor absorbs energy, and for emitting energy as photons, characterized in that the dwell time of an exciton that is to be transferred from the polymer to the acceptor is longer than the time for transferring said exciton from the polymer to the acceptor, by satisfying the equation  
     k ET   pp &lt;k ET   pd ,  
     wherein k ET   pp  is the rate constant of the energy transfer at λ between two chromophores of the polymer, k ET   pd  is the rate constant of the energy transfer at λ between the polymer and the acceptor. If the energy transfer processes in the polymer-acceptor system can be described by Förster theory the above equation can be rewritten as  
           R   _     pd     &lt;       R   0   pd     ·       (       τ   ET   pp       τ   n       )       1   /   6                       
 
     {overscore (R)} pd  is the mean distance between the polymer and the acceptor, R 0   pd  is the Förster radius, and τ ET   pp  and τ n  are the experimental lifetimes of a single chromophore and of the plurality of chromophores of the polymer, respectively.

[0001] The invention pertains to an (electro)luminescentpolymer-acceptor system comprising a polymer with a plurality ofchromophores and an acceptor for transferring excitation energy, to amethod of making such an (electro)luminescent polymer-acceptor system,and to a method for tuning the color in an (electro)luminescent device.(electro)luminescent is short for luminescent and electroluminescent inparticular.

[0002] In polymer light emitting diodes (PLED) polymeric luminescentsubstances are used to generate a light. Such devices are known, forinstance from EP 1,043,382. In such devices the polymeric material isused as such for emitting light, or the polymer is mixed with othermaterials, such as organic dyes, in a light emitting layer. Adisadvantage of such devices is that for the purpose of obtaining fullcolor emission a large variety of specific luminescent polymers must bemade. Such specific polymers are disclosed, for instance, in U.S. Pat.No. 5,712,361. It is known that the luminescence character of suchpolymers can be changed by mixing the polymer with a luminescent dye,see for instance EP 892,028. However, such mixtures are obtained bytrial and error and it is not known in advance which mixtures lead toefficient luminescence. Further, there is no reason that such arbitrarymixtures contribute to the stability of the luminescent system. It is anobject of the present invention to find a method for obtainingpolymer-acceptor systems with optimum efficiency, stability, colorpurity, and to find the conditions which such an efficientpolymer-acceptor system must satisfy.

[0003] The process of excitation energy migration in a polymer dopedwith a dye is not fully understood. The most pertinent reference in thisrespect is a publication by List et al., Chemical Physics Letters, 325(2000), 132-138. These authors come to the conclusion that theexcitation energy migration between a polymeric host and guest has to beexplained by the sum of at least two processes. First atemperature-dependent migration process of singlet excitons which can beof Dexter or Coulomb type and a second temperature-independent transferof the singlet exciton, which is of Förster dipole-dipole interactiontype. However, these authors do not disclose the requirements that arenecessary to obtain optimum luminescent efficiency at maximum stability.Applying the Förster theory, for instance as suggested by List et al,the skilled person comes to the conclusion that maximum overlap of theemission spectrum of the donor and the absorption spectrum of theacceptor is necessary to obtain the highest energy transfer efficiency.However, experiments performed by us unexpectedly showed that this isnot the case. On the contrary, under these conditions the efficiencyappeared to be very low.

[0004] According to the present invention the main issues in polymerluminescent materials, including (electro)luminescent materials, i.e.the stability, efficiency, and the color gamut of the presently knownsubstances, can be addressed by using acceptors in luminescent polymers.The stability is effectively increased by incorporation of an acceptor,which depopulates in a highly efficient manner the (reactive) excitedstate of the luminescent polymer. When a very stable emissive dye isapplied, such as a laser dye, the stability of the material issignificantly improved. The second important advantage of the presentinvention is that luminescent acceptors can be used for the realizationof a full color display. According to the invention the dyes are chosento provide the optimum emission wavelength with respect to the desiredcolor purity. The fact that several emissive acceptors can each beincorporated into a particular polymer for obtaining different emissionwavelengths is an additional advantage of the invention. In this way foreach of the three basic colors required for a full color display thesame device structure can be used.

[0005] In the (electro)luminescent polymer-acceptor system of theinvention, the acceptor is selected from an organic dye, an oligomer, apolymer, a luminescent nanoparticle, such as a quantum dot, orcombinations thereof.

[0006] If used in an electroluminescent device the polymer has to becapable of transporting charge carriers, such as holes and/or electrons.Suitably, the polymer may be an, at least partially, conjugated polymer.

[0007] The invention therefore pertains to an (electro)luminescentpolymer-acceptor system comprising a polymer with a plurality ofchromophores doped with an acceptor for transferring excitation energyfrom the polymer to the acceptor wherein at least one wavelength of thepolymer emission is a wavelength □ at which the acceptor absorbs energy,and for emitting energy as photons, characterized in that the dwell timeof an exciton that is to be transferred from the polymer to the acceptoris longer than the time for transferring said exciton from the polymerto the acceptor, by satisfying the equation

k_(ET) ^(pp)<k_(ET) ^(pd),

[0008] wherein k_(ET) ^(pp) is the rate constant of the energy transferat λ between two chromophores of the polymer, k_(ET) ^(pd) is the rateconstant of the energy transfer at λ between the polymer and theacceptor.

[0009] If the energy transfer processes of the polymer-acceptor systemcan be described by Forster theory, the above relationship can berewritten as${\overset{\_}{R}}^{pd} < {R_{0}^{pd} \cdot \left( \frac{\tau_{ET}^{pp}}{\tau_{n}} \right)^{1/6}}$

[0010] wherein {overscore (R)}^(pd) is the mean distance between thepolymer and the acceptor, R₀ ^(pd) is the Förster radius, and τ_(ET)^(pp) and τ_(n) are the experimental lifetimes of a single chromophoreand of the plurality of chromophores of the polymer, respectively. TheF{overscore (o)}rster radius is thereby defined as the separationbetween a donor and an acceptor for which the rate of energy transferbetween the excited donor and the ground state acceptor and the inherentrate of deactivation of the excited donor are equal. The dwell time isthe time that an exciton spends on a certain polymeric chromophore. Therate constant of the energy transfer between two chromophores of thepolymer is identical to the reciprocal value of the lifetime of theenergy transfer at a certain wavelength λ in the polymer.

[0011] The ratio k_(ET) ^(pd):k_(ET) ^(pp) is preferably greater than 5,more preferably greater than 15, and most preferably greater than 20.For reasons of efficiency, it is preferred that the λ for which theratio is 1 lies at the high energy side in the area of overlap of theemission spectrum of the polymer and the absorption spectrum of theacceptor, or at an even higher energy. A way to tune the color of apolymer-based (electro)luminescent device is to incorporate luminescentdyes (or more generally luminescent acceptors) into the polymer. Whenthe dye and the polymer satisfy the above conditions, upon excitation ofthe polymer the energy will be transferred to the dye, which process isknown as excitation energy transfer (EET), followed by luminescence fromthe dye. By using different dyes, different colors can be obtained. Amajor advantage of such suitable combinations of polymer and acceptor sis that the emission properties are decoupled from the chargetransporting and excitation properties of the polymer. The principle ofthis invention is based on the known Förster theory for Coulomb dipolarinteraction. The standard formulation of this theory is given by theFörster equation: $\begin{matrix}{k_{ET} \propto {\frac{1}{\tau_{D}} \cdot \left( \frac{R_{0}}{R} \right)^{6}}} & (1)\end{matrix}$

[0012] In this relation k_(ET) is the rate constant for energy transfer,τ_(D) the experimental lifetime of the donor in the absence of anacceptor, and R the distance between the donor and the acceptor. R₀ isthe Förster radius, which for this type of polymer-acceptor systems isapproximately 15 Å.

[0013] Using Förster's theory the rate constants of the energy transferbetween the chromophores, which constitute a disordered polymer (pptransfer) and the energy transfer between a chromophore of the polymerand the acceptor, for instance a dye (pd transfer), is given by:$\begin{matrix}{k_{ET}^{pp} \propto {\frac{1}{\tau_{D}^{pp}} \cdot {\left( \frac{R_{0}^{pp}}{{\overset{\_}{R}}^{pp}} \right)^{6}\bigwedge\quad k_{ET}^{pd}}} \propto {\frac{1}{\tau_{D}^{pd}} \cdot \left( \frac{R_{0}^{pd}}{{\overset{\_}{R}}^{pd}} \right)^{6}}} & \left( 2 \right.\end{matrix}$

[0014] wherein {overscore (R)} is the mean distance between the speciesinvolved in the energy transfer process.

[0015] The rate for the energy transfer (Φ_(ET)) is:

Φ_(ET) =k _(ET) ·[D*][A]  (3)

[0016] wherein D* stands for the concentration of excited donors and Afor the concentration of acceptors. Thus formula (2) can be written as:

Φ_(ET) ^(pp) =k _(ET) ^(pp) ·[p _(i) *][pj] {circumflex over ( )} Φ_(ET) ^(pd) =k _(ET) ^(pd) ·[p _(i) *][d]  (4)

[0017] wherein p and d denote the concentrations of the polymericchromophores and the dye (acceptor) molecules, respectively. The pdtransfer is more efficient than the pp transfer when

Φ_(ET) ^(pp)<Φ_(ET) ^(pd), thus: $\begin{matrix}{k_{ET}^{pp} < {\frac{1}{\tau_{n}} \cdot \left( \frac{R_{0}^{pd}}{{\overset{\_}{R}}^{pd}} \right)^{1/6}}} & (5)\end{matrix}$

[0018] in which formula d and p are not included as they are constantfor all samples. By definition $\begin{matrix}{k_{ET}^{pp} \equiv \frac{1}{\tau_{ET}^{pp}}} & (6)\end{matrix}$

[0019] Thus formulae (5) and (6) give: $\begin{matrix}{{\overset{\_}{R}}^{pd} < {R_{0}^{pd} \cdot \left( \frac{\tau_{ET}^{pp}}{\tau_{n}} \right)^{1/6}}} & (7)\end{matrix}$

[0020] The term τ_(ET) ^(pp) describes the lifetime of the intra-polymerexciton transfer, or in other words, the transfer time of an excitonfrom chromophore i to chromophore j. This time is also called the dwelltime of chromophore i (τ_(i) _(dwell)). Thus the dwell time is the timethat an exciton stays on a certain chromophore.

[0021] A disordered polymer can be described as an ensemble (plurality)of chromophores differing in conjugation length and/or chemicalsurroundings. The dwell time of an exciton on a certain chromophoredepends on the excited state energy of this particular chromophore. Thedwell time increases when the energy of the excited state decreases.Equation (7) can now be transformed to: $\begin{matrix}{\frac{{\overset{\_}{R}}^{pd}}{R_{0}^{pd}} < \left( \frac{\tau_{i}^{dwell}}{\tau_{n}} \right)^{1/6}} & (8)\end{matrix}$

[0022] Since the dwell time cannot be longer than the experimentallifetime τ_(n) of the polymer, the above ratio is always smaller than 1.This is shown in FIG. 1 where the mean polymer-dye distance (<R>^(pd))relative to the Förster radius as a function of the ratio between thedwell time and the experimental lifetime of the polymer is given.

[0023] The value for the Förster radius (R₀ ^(pd)) can be obtained fromthe steady state emission spectrum of the undoped polymer and theabsorption spectrum of the dye. This value is approximately the same(about 15 Å) for similar systems as described herein. The value of τ_(n)can be obtained from time-resolved measurements on the emission from anundoped polymer. τ_(n) Is the lifetime of this emission which isdependent on the photon energy and which can vary by two orders ofmagnitude between high and low energy photons that are emitted from thepolymer.

[0024]FIG. 1 shows that the energy transfer from the polymer to anacceptor is very inefficient when the dwell time is much shorter thanthe lifetime of the polymer. Energy transfer from the polymer to theacceptor can only compete with the intra-polymer exciton transfer whenthe dwell time and transfer time become comparable.

EXPERIMENTAL PROCEDURE

[0025] An experimental procedure is described by which one can determineif a polymer-acceptor system satisfies the condition that is describedin this description. The term “working” means that under operation adevice containing the polymer-acceptor combination emits photons fromthe acceptor (dopant).

[0026] Provided that there is energetic resonance between a polymer andan acceptor (spectral overlap between the polymer emission and theacceptor absorption) excitons will be transferred from the polymer tothe acceptor when the dwell time of an exciton on a polymericchromophore is longer than the transfer time of this exciton to theacceptor. As mentioned before, the dwell time is the time that theexciton spends on a certain polymeric chromophore and this can bedetermined by measuring the lifetime of the emission originating fromthe energy level belonging to the particular chromophore. The transfertime between the polymer and the acceptor can be determined by measuringthe rise time of the acceptor emission. By comparing the lifetime of theemission from a certain polymer energy level to the rise time of theacceptor emission one can establish whether transfer of an exciton fromthis particular polymer energy level can occur. A stepwise descriptionof the experimental procedure is:

[0027] A polymer-acceptor combination should have a spectral overlapbetween the polymer emission and the acceptor absorption. First thespectral position of this overlap is determined by measuring theemission spectrum of the pure polymer and the absorption spectrum of thepure acceptor (dopant, dye).

[0028] Next it is determined whether the polymer-acceptor combinationworks because it satisfies the condition which is mentioned in thisdescription: transfer of excitons between a polymer and an acceptor onlyoccurs when the rate constant of transfer of the exciton between twochromophores of the polymer, that is within the polymer, k_(ET) ^(pp),is smaller than the transfer rate constant, k_(ET) ^(pd) of this excitonfrom the polymer to the acceptor, i.e. k_(ET) ^(pp)<k_(ET) ^(pd).

[0029] As mentioned above, the k_(ET) ^(pp) at a particular wavelengthof emission is determined by measuring the lifetime at that wavelengthof emission of the polymer as such, that is without the acceptor beingpresent, lifetime being defined as the time at which the intensity hasdropped to 1/e the maximum (initial) intensity. Such rate constants aremeasured over the entire range of spectral overlap as any of the polymerenergy levels in this range could be involved in the transfer process.These measurements are done with an order of magnitude accuracy.

[0030] Finally, the transfer rate constant k_(ET) ^(pd), which is aproperty of the combined polymer-acceptor system, is determined bymeasuring the rise time at a wavelength at which only the emissionoriginating from the acceptor is observed, the rise time being measuredwith a similar (order of magnitude) accuracy, rise time being defined asthe time at which the intensity has risen to 1/e its maximum intensity.

[0031] If anywhere in the spectral overlap region the lifetime of thepolymer emission is longer than the rise time of the acceptor emission,the polymer-acceptor combination satisfies the condition mentioned inthis invention.

[0032] Thus the invention also pertains to a method of making apolymer-acceptor system comprising the steps of selecting a polymer andan acceptor, such that at least one wavelength of the emission spectrumof the polymer overlaps with at least one wavelength of the absorptionspectrum of the acceptor, and whereby the dwell time of an exciton thatis to be transferred from the polymer to the acceptor is longer than thetime for transferring said exciton from the polymer to the acceptor,after which said selected polymer doped with said selected acceptor isapplied in an (electro)luminescent device.

[0033] In another aspect, the invention also provides a method fortuning the color in an (electro)luminescent device by using an(electro)luminescent polymer-acceptor system for transferring excitationenergy from a polymer to an acceptor wherein at least one wavelength ofthe polymer emission overlaps with a wavelength at which the acceptorabsorbs energy, and for emitting energy as photons whereby the dwelltime of an exciton that is to be transferred from the polymer to theacceptor is longer than the time for transferring said exciton from thepolymer to the acceptor, characterized in that at least two polymerswith a plurality of chromophores are used, which polymers can be thesame or different, and at least one of the polymers is doped with anacceptor to form a combination therewith, each of the polymer andacceptor combinations satisfying the equations

k_(ET) ^(pp)<k_(ET) ^(pd), and${\overset{\_}{R}}^{pd} < {R_{0}^{pd} \cdot \left( \frac{\tau_{ET}^{pp}}{\tau_{n}} \right)^{1/6}}$

[0034] wherein k_(ET) ^(pp) is the rate constant of the energy transferat λ between two chromophores of the polymer, k_(ET) ^(pd) is the rateconstant of the energy transfer at λ between the polymer and theacceptor, {overscore (R)}^(pd) is the mean distance between the polymerand said acceptor, R₀ ^(pd) is the Förster radius, and τ_(ET) ^(pp) andτ_(n) are the experimental lifetimes of a single chromophore and of theplurality of chromophores of the polymer, respectively.

[0035] The polymer-acceptor system of the invention can be used inpolymer light emitting diodes (LED), polymer light emitting cells (LEC),displays in general, and in plastic electronics (such as field effecttransistors).

[0036] The invention is illustrated by means of the followingnon-restrictive example.

EXAMPLE 1

[0037] The polymer poly (2-(meta-3,7dimethyloctyloxy-phenyl)-p-phenylene vinylene, which is a green emittingpolymer with a repeating unit of the structural formula:

[0038] and the red emitting organic dye acceptor (dopant),4,4-difluoro-3,5-bis[2-(5-methylthiophene)]-4-bora-3a,4a-diaza-s-indacene,with the structural formula:

[0039] were used for making the polymer-acceptor system of theinvention.

[0040] First, a solution of the polymer was prepared by dissolving aspecific amount of the polymer in toluene to yield a solution whichcontains 4 g polymer per 1 I of toluene (0.4% weight-to-volume ratio).This solution was stirred overnight at room temperature. Secondly, asmall amount of the dye was dissolved in toluene. The concentration ofthis dye solution was chosen such that only a few μl had to be added toabout 5 ml of the polymer solution to give a 0.75% dye-to-polymer weightratio. The dye-polymer solution was spin coated onto a glass substrategiving a layer thickness of about 70 nm.

[0041] Photoluminescence emission spectra of the undoped green emittingpolymer (dashed line) and of the same polymer doped with the redemitting organic dye (full line) upon excitation with light of 410 nmare shown in FIG. 2. The photoluminescence excitation spectra asrecorded at the maximum of the emission band were identical for bothsamples indicating that only the polymer is photoexcited and that theemission from the dye is due to energy transfer from the polymer to thedye. From FIG. 2 it can also be seen that in the dye-doped polymer stilla remainder of the polymer emission is visible. If this remainingemission band is compared to the original emission band it is clear thatthe former is shifted to higher energies with respect to the latter.This means that in the dye-doped polymer, the polymeric chromophoreswith a relatively high HOMO-LUMO distance are still emitting, althoughan energy acceptor is present. Apparently, only the polymericchromophores with a lower HOMO-LUMO distance are transferring theirenergy to the organic dye because the dwell time of the exciton on thesechromophores is long enough to enable transfer of the exciton to theorganic dye.

[0042] As can be seen in FIG. 3, the absorption spectrum of the redemitting organic dye overlaps the emission spectrum of the greenemitting polymer (dashed line) at its low energy side. This is inagreement with the observations made from FIG. 2. The only polymericchromophores that are capable of transferring energy to the organic dyeare situated at the low-energy side of the polymer emission band, whichis at the same point where the organic dye has its highest absorbance.

Synthesis of4,4-difluoro-3,5-bis[2-(5-methylthiophene)]-4-bora-3a,4a-diaza-s-indacene

[0043] bromosuccinimide (9.08 g) was added to a mixture of20-methylthiophene (5.00 g) in 25 ml of THF (tetrahydrofuran) at 0° C.The mixture was kept in the dark and stirred overnight. The solvent wasevaporated, the precipitate was dissolved in 30 ml of diethyl ether, andwashed with a saturated sodium hydrogencarbonate solution. The organicsolution was dried over magnesium sulfate, filtered, and concentrated togive a crude oily product, which was purified with vacuum distillationto give a colorless oil (5-bromo-2-methylthiophene) in 82% yield.

[0044] mixture of 6-bromo-2-naphthol (10.0 g), 3-bromopropanol (9.4 g)and potassium hydroxide (3.0 g) in 50 ml of ethanol was refluxed for 16h. The mixture was washed with diethyl ether and water. The combinedorganic layers were dried, filtered, and concentrated. The crude productwas crystallized from ethanol to give6-bromo-2-(3-hydroxypropyloxy)-naphthalene in 40% yield.

[0045] o N-tert-butoxycarbonyl-2-trimethylstannylpyrrole (2.0 g;prepared according to S. Martina et al., Synthesis, 1991, 613) and5-bromo-2-methylthiophene (1.07 g) in 20 ml DMF (N,N-dimethylformamide)was added dichloro bis (triphenylphosphino)palladium(II) (87 mg) underan argon atmosphere. The mixture was heated at 70° C. for 16 h. Aftercooling the mixture was washed with diethyl ether and water. Thecombined organic layers were dried (MgSO₄), filtered, and concentrated.The crude product was purified by column chromatography (silica,hexane/dichloromethane, 66/34,vlv) to give a pure yellow oil in 32%yield [2-(2-(5-methylthiophene)-N-tert-butoxycarbonylpyrrole].

[0046] To N-tert-butoxycarbonyl-2-trimethylstannylpyrrole (3.0 g) and6-bromo-2-(3-hydroxypropyloxy)naphthalene (2.55 g) in 20 ml of DMF wasadded dichloro bis(triphenylphosphino)palladium(II) (64 mg) under anargon atmosphere. The mixture was heated at 70° C. for 16 h. Aftercooling the mixture was washed with diethyl ether and water. Thecombined organic layers were dried (MgSO₄), filtered, and concentrated.The crude product was purified by column chromatography (silica,hexane/dichloromethane, 2/98, v/v) to give a pure oil in 60% yield[2-(6-(3-hydroxypropyloxy)-naphthyl)-N-tert-butoxycarbonylpyrrole]. Tothis oil (0.5 g) in 10 ml of DMF was added dropwise phophorusoxychloride(0.42 g) at 0° C. under an argon atmosphere. The mixture was heated at60° C. for 2 h. After cooling the mixture was neutralized with aqueoussodium hydroxide (1 M) and heated at 80° C. for 1 h. After cooling theprecipitate was filtered off and purified by column chromatography(silica, methanol/dichloromethane, 1/99,v/v) to give a 75% yield of5-formyl-2-(6-(3-chloropropyloxy)-naphthyl)-N—H-pyrrole.

[0047] 2-(2-(5-methylthiophene)-N-tert-butoxycarbonylpyrrole (0.50 g)was converted to 2-(2-(5-methylthiophene)-N—H-pyrrole by heating at 190°C. for 15 min in an argon atmosphere. After cooling to room temperaturedichloromethane (40 ml) and5-formyl-2-(6-(3-chloropropyloxy)-naphthyl)-N—H-pyrrole (0.60 g) wereadded.

[0048] Phosphorusoxychloride (180 μl) was added dropwise. After stirringat room temperature for 16 h, N,N-diisopropylethylamine (1.35 ml) andboron trifluoride diethyl etherate (1.0 ml) were added and the mixturewas stirred for another 2 h. The reaction mixture was washed with brine,dried, filtered, concentrated, and purified by column chromatography(silica; hexane/chloroform 40/60 v/v) giving 14% yield of4,4-difluoro-3,5-bis[2-(5-methylthiophene)[-4-bora-3a,4a-diaza-s-indacene.

[0049] Characteristic ¹H-NMR (CDCl₃) signals (ppm) are: 7.98 (d, 2H,J=3.8 Hz); 7.01 (s, 1H); 6.96 (d, J=4.2 Hz, 2H); 6.85 (dd, J=3.8 Hz,2H); 6.74 (d, 2H, J=4.2 Hz); 2.55 (s, 6H).

Synthesis of poly(2-(meta-3.7 dimethyloctyloxy-phenyl)-p-phenylenevinylene

[0050] In a dry threeneck flask a solution of2,5-bis(chloromethyl)-1(meta-3,7dimethyloctyloxyl-phenyl) benzene (15.03gr, 3.69 10⁻² mol) in 2 liters of dry dioxane (distilled) was degassedfor 1 hour by passing through a continuous stream of nitrogen and heatedto 100° C. The base (24.76 gram, 0.22 mol, 6 eq.) was added in twoportions dissolved in dry and degassed dioxane (2 times 150 ml). Thesolution was heated for two hours at 100° C. A small amount (20 ml) ofacetic acid was added to quench the base. The colour changes from greento fluorescent green/yellow. The solution is precipated in water. Afterfiltration the raw polymer is dissolved in THF by heating for 2 hours at60° C. and precipitated in methanol. This procedure is repeated. Thepolymer is dried in vacuo and the yield is 8 grams of polymer (65%) inyellow fibers.

[0051] The following characteristics apply:

[0052]GPC: against polystyrene standards UV detection M_(n)=3.0 10⁵g/mol Mw =1.5 10⁵ g/mol. PL ^(λ) _(max)=525 nm ¹H-NMR (CDCl₃)δ(ppm)=7.9-6.8 (br. M, 9H), 4.2-3.9 (br. M, 2H) 2.0-1.0 (br, m., 13H)0.9 (s, 6H)

1. An (electro)luminescent polymer-acceptor system comprising a polymerwith a plurality of chromophores doped with an acceptor for transferringexcitation energy from the polymer to the acceptor wherein at least onewavelength of the polymer emission is a wavelength λ at which theacceptor absorbs energy, and for emitting energy as photons,characterized in that the dwell time of an exciton that is to betransferred from the polymer to the acceptor is longer than the time fortransferring said exciton from the polymer to the acceptor, bysatisfying the equation k_(ET) ^(pp)<k_(ET) ^(pd), wherein k_(ET) ^(pp)is the rate constant at λ of the energy transfer between twochromophores of the polymer, k_(ET) ^(pd) is the rate constant at λ ofthe energy transfer between the polymer and the acceptor.
 2. The(electro)luminescent polymer-acceptor system of claim 1 wherein thepolymer comprises a substituted or unsubstituted phenylene-vinylene,phenylene, phenylene-ethyne, triphenylamine, thiophene, vinylcarbazole,fluorene, or a spirofluorene.
 3. (electro)luminescent polymer-acceptorsystem of claim 1 wherein the polymer is chemically bonded to theacceptor through a spacer.
 4. A method of making a polymer-acceptorsystem comprising the steps of selecting a polymer and an acceptor, suchthat at least one wavelength of the emission spectrum of the polymeroverlaps with at least one wavelength of the absorption spectrum of theacceptor, and whereby the dwell time of an exciton that is to betransferred from the polymer to the acceptor is longer than the time fortransferring said exciton from the polymer to the acceptor, after whichsaid selected polymer is doped with said selected acceptor and appliedin an (electro)luminescent device.
 5. A method for tuning the color inan (electro) luminescent device by using an (electro)luminescentpolymer-acceptor system for transferring excitation energy from apolymer to an acceptor wherein at least one wavelength of the polymeremission overlaps with a wavelength λ at which the acceptor absorbsenergy, and for emitting energy as photons whereby the dwell time of anexciton that is to be transferred from the polymer to the acceptor islonger than the time for transferring said exciton from the polymer tothe acceptor, characterized in that at least two polymers with aplurality of chromophores are used, which polymers can be the same ordifferent, and at least one of the polymers is doped with an acceptor toform a combination therewith, each of the polymer and acceptorcombinations satisfying the equations k_(ET) ^(pp)<k_(ET) ^(pd), whereink_(ET) ^(pp) is the rate constant of the energy transfer at λ betweentwo chromophores of the polymer, k_(ET) ^(pd) is the rate constant ofthe energy transfer at λ between the polymer and the acceptor.
 6. Themethod of claim 5 wherein three polymers with a plurality ofchromophores are used, which polymers can be the same or different, andwherein at least two of the polymers are doped with a different acceptorto form a combination therewith.